Direct numerical simulations of turbulent boundary layers over calcareous biofouling*

It is well established today that biofouling on ships increases the hull roughness, causing increased frictional resistance and fuel consumption, as well as decreased top speed and range.  Today there is a pressing need to develop predictive tools that can assess the impact of various types of fouling and coverage level on the frictional resistance of naval vessels.  Most scaling laws and correlations integrated in the models utilized in such assessments were not developed with sufficient data representative of ship roughness. Surfaces covered by barnacles and/or tubeworms, for example, have much higher skewness (Sk) and lower effective slope (ES) than other surfaces used to develop existing correlations.  The primary goal of this work is to identify geometric parameters on surface roughness topologies found on ships that encapsulate the drag-producing physics.  In particular, we will report Direct Numerical Simulations (DNS) of turbulent boundary layers over biofouled surfaces synthezied using barnacles and/or tubeworms. A highly-efficient, in-house, solver based on an immersed boundary formulation is utilized.  We will report detailed flow statistics for a variety of surfaces while particular emphasis will be placed on the identification/impact of the secondary flow patterns on the flow statistics and outer-layer similarity.